The World War II program to develop an atomic bomb was the largest secret project ever undertaken by the U.S. government. But newly-declassified documents reveal how it hard it was to keep things secret as the weapon neared completion. Information leaks were everywhere, even in church sermons.

Trinity Test plutonium bomb image courtesy of Truman Library.

These detailed accounts have been made public on the website of the Department of Energy, which has posted the 36-volume, official history of the Manhattan Project, which had been commissioned by General Leslie Groves in late 1944. Among the most intriguing set of documents, released last month, is the volume about intelligence and security, which reveals:

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"Since September 1943, investigations were conducted of more than 1,500 'loose talk' or leakage of information cases and corrective action was taken in more than 1,200 violations of procedures for handling classified material…. Complete security of information could be achieved only by following all leaks to their source."

Counterintelligence officials had their work cut out for them.

A Top Top Secret Project

Efforts to keep a lid on atomic energy research had begun even before the Manhattan Project had started. In 1939, refugee scientists—mindful of the growing threat posed by Nazi Germany—urged their U.S. colleagues to undertake voluntary censorship of published studies concerning uranium fission. Initially, they rejected the idea—but as one European country after another fell to the Germans in 1940, the U.S. scientific community came to understand the importance of self-censorship. The Division of Physical Sciences of the National Research Council established a committee that succeeded in convincing most scientists to withhold publication of papers on sensitive subjects.

Still, occasional newspaper articles wrote about the potential applications of uranium fission in warfare. One such article, sympathetic to the plight of Europe, appeared in the March 18, 1941 edition of the Montana Standard:

It is known that there is enough power in one portion of uranium-235 the size of a pear to shoot the Empire State Building in the air with the speed of a rocket. It would be more than two million times as possible as one 1,000-pound air bomb of the type used by the Nazis in bombing London.

But nature has used her usual foresight in guarding such potential annihilation. Scientists admit it is impossible to separate uranium-235 from uranium-238. It is not that science has not figured out a method. It has. But the apparatus would be so complicated there is not now in existence enough scientists to set it up, even though they were to work a lifetime doing it.

Although physicists continued to play up the "impossible task" of separating sufficient amounts of uranium-235 to construct a bomb, reports and rumors of such a secret weapon continued to pop up in the press. Finally, in 1943, the director of the wartime Office of Censorship sent a special request to editors and broadcasters to not report on any rumors of "secret weapons" and to withhold any information on:

Production or utilization of atom smashing, atomic energy, atomic fission, atomic splitting, or any of their equivalents.

The use for military purposes of radium or radioactive materials, heavy water, high voltage discharge equipment, cyclotrons.

The following elements or any of their compounds: plutonium, uranium, ytterbium, hafnium, protoactinium, radium, thorium, deuterium.

But, the greatest challenge to secrecy was the expansion of the Manhattan Project itself. As noted in the book, Counterintelligence in World War II:

The modest security system sufficed until, in the spring of 1942, with the start of the uranium program's rapid expansion. The letting of numerous contracts with industrial firms; the employment and interaction of ultimately tens of thousands of workers, scientists, and engineers; and the formation of complex organizations to construct and operate the large-scale production plants and their atomic communities—[all of this] enormously complicated the problems of security just at the time the Army undertook its new role as project administrator. Although these measures were necessary for the more rapid achievement of a successful fission weapon, they also tended to weaken security.

And it was at this time that the Manhattan Project began springing leaks.

Loose Lips Sink Ships

The declassified official history of the Manhattan Project is fascinating in that it reveals the tremendous amount of resources invested in tracking down the source of each and every reported leak—which encompassed more than 1,500 investigations.

And, the documents include several examples of the type of "loose talk" and careless behavior that occurred more frequently as the program to build the atomic bomb expanded. All of the cases had to be investigated, sometimes revealing false alarms, other times revealing potentially serious breeches in security.

Here's a sampling of some of the cases discussed in the documents:

1) A Naval lieutenant at a dinner party in March 1945 openly wondered "when we would use the atomic bomb," adding that "only about ten pounds of U-235 are needed to end the war." He also said that "several thousand persons were working on it in Tennessee."

When agents interviewed the lieutenant, he recalled a 1942 lecture given at the chemistry department at Harvard regarding the possibilities of atomic power, and he had since discussed the subject with friends and had read many speculative articles in technical magazines. He stated that "anyone traveling for the government realized there was a great secret project there" and he merely assumed that it was engaged in the development of atomic power.

2) In the fall of 1944, an employee of a New York firm, doing engineering work for the project, was taking a train from New York to Oak Ridge carrying a highly secret file of engineering details. He arrived at Penn Station with several minutes to spare before the train departed, so he used the time to make a last minute call to his wife from a telephone booth.

After finishing the call, he headed for the train and discovered that he didn't have the secret papers with him. He decided to catch the train, so he called his office and requested that someone come down to the station to look for the papers. The security agent for the company rushed to the station and made a frantic search, finally locating them at the information booth. The employee who had lost the papers was ordered to return to New York, where he was "soundly reprimanded" and fired by the company.

3) One case concerned a pamphlet titled Startling Power. In the winter of 1945, a patent engineer secured a copy of the pamphlet, which had been published by the Good News Publishing Company in Chicago and was distributed by the Moody Bible Institute. The pamphlet declared that, "Uranium 235, extracted from natural uranium ore, promises to make all of our power sources mere child's toys by comparison. Professor John R. Dunning, Columbia University Leader in Atomic Energy Research, has stated that the natural substances from which Uranium 285 is extracted abound abundantly in the earth and throughout many sections of the world." However, the pamphlet continued, "We must not overlook the far more vital and assured fact that God has given to Christians the gift of the Holy Spirit with energies far more dynamic than those of exploding atoms or mysterious elements."

Upon reading this pamphlet, the patent engineer concluded that U-235 merited investigation by his company. His boss contacted the prominent physicist Arthur Compton to find out more about the potential applications of uranium, which triggered an investigation. Security officials were relieved to learn the source of the inquiry was a harmless reading of a religious tract.

Religious sermons were occasionally investigated over the years, such as when a Lutheran minister declared to his flock that, "One of the developments in the field of science today is a new source of energy called uranium-235. But regardless of the power of uranium 235 or other energy which science may discover, it will never be powerful enough to comfort us in affliction or strengthen us in despair. We must search out the Lord for those things." Discrete inquires revealed that this, and other sermons like it, were taken from the same pamphlet, Startling Power.

4) An employee at Oak Ridge wrote a letter to her uncle, telling him the war would be over quickly, when "the product" being produced was finally used. Unfortunately, she dropped the letter on a bus prior to mailing it. She admitted to intelligence agents that, in her position as a confidential secretary, she had "acquired considerable information about the work of the project, but had been very foolish to reveal any of the information to her uncle." She was fired.

Reading these few examples reveals how vulnerable the Manhattan Project was to discovery, despite its unprecedented level of secrecy. As Alex Wellerstein, an historian of science who specializes in nuclear weapons has previously observed:

There were a tremendous number of puzzle pieces out there for an enemy power to notice and put together regarding the bomb effort. It was not quite so perfectly secret as we often talk of it as being. We know it was possible to put some of the pieces together, because the Soviets did it, and even a few others did it. General Groves wanted a hegemonic, all-encompassing, all-controlling secrecy regime. Understandably, he couldn't accomplish that — but he pulled off just enough that, with a bit of luck, the project stayed more or less below the water line.